Motor starter unit with interlock means for selectively mountable circuit breaker operating mechanism

ABSTRACT

A motor starter unit is mountable selectively on opposite sides of a stack of bus bars of an electrical panelboard and includes a reversibly positionable circuit breaker operating mechanism. Interlocks are provided to prevent opening of a cover of the motor starter unit when a handle of the operating mechanism is in ON position, unless an interlock-defeating screw is first turned, and to prevent movement of the handle to ON position when the cover is open.

United States Patent Rys [451 July 18, 1972 [541 MOTOR STARTER UNIT WITHINTERLOCK MEANS FOR SELECTIVELY MOUNTABLE CIRCUIT BREAKER OPERATINGMECHANISM [72] Inventor: 'ladeusz J. Rys, Lexington, Ky.

[73] Assignee: Square D Company, Park Ridge, 111.

[22] Filed: April 28, 1971 211 App1.No.: 138,137

52 us. 01. ..200/50A 511 1111.01... ...H01h9/22 [58] FieldofSearch..200/50A;3l7/il9; 74/503 [56] References Cited UNITED STATES PATENTS3,028,459 4/1962 Norden ..200/50 A 3,213,219 10/1965 Mrenna et al..200/50 A Primary Examiner-J. R. Scott Attorney-Harold J. Rathburn andPaul J. Rose ABSTRACT 10 Claims, 25 Drawing Figures PATENTEU JUL18I9723,678,230

sum 1 OF 6 2 TADEUSZ J. RYS

PATENTEU JUL18l972 3,678,230

INVENTOR.

TADEUSZ J. RYS

PAIENTEU JUL] 8 m2 3, 7 ,230 SHEET u or '5 INVENTOR. 46b E 49 48 460TADEUSZ J. RYS

PATENTEDJUUBISTZ 3.678.230

sum 5 OF 6 FIG. l8

INV EN TOR.

TADEUSZ J. RYS

msmsnwuemz 3.678.230

SHEET 6 OF 5 FIG. 2|

IN V EN TOR.

FIG. 25

TADEUSZ d. RYS

MOTOR STARTER UNIT WITH INTERLOCK MEANS FOR SELECTIVELY MOUNTABLECIRCUIT BREAKER OPERATING MECHANISM An electric circuit breaker forminga separable component of a motor starter unit is mountable selectivelyon opposite sides of a stack of bus bars of an electrical panelboard,being rotated through an angle of one hundred eighty degrees when movedfrom one side of the bus bars to the other. An object of the inventionis to provide interlocking means for a motor starter unit, the unitbeing operatively associable with such a circuit breaker and panelboardand also mountable selectively on opposite sides of the stack of busbars, but without being rotated when moved from one side of the bus barsto the other. Another object is to provide a motor starter unitincluding a front cover, a reversibly positionable circuit breakeroperating mechanism, and interlocking means preventing normal opening ofthe cover when a handle of the circuit breaker operating mechanism is inON position.

A further object is to provide a motor starter unit including a frontcover, a reversibly positionable circuit breaker operating mechanism,and interlocking means preventing movement of a handle of the circuitbreaker operating mechanism to ON position when the cover is open.

These and other objects will become apparent when the followingspecification is considered along with the accompanying drawings inwhich:

FIG. 1 is a front view of a motor starter unit constructed in accordancewith the invention and with a handle of a circuit breaker operatingmechanism in an ON position;

FIG. 2 is a fragmentary bottom view of the motor starter unit ofFIG. l;

FIG. 3 is a fragmentary front view similar to the upper portion of FIG.1, but with a front cover of the motor starter unit removed;

FIG. 4 is a fragmentary front view similar to FIG. 3, but with a circuitbreaker operating mechanism of the motor starter unit reversedend-for-end and shifted toward the right from the position shown in FIG.3;

FIG. 5 is a fragmentary right side view of the motor starter unit ofFIG. 1;

FIG. 6 is a view of the circuit breaker operating mechanism looking inthe direction of arrows 6-6 in FIG. 3;

FIG. 7 is a view of the circuit breaker operating mechanism from theright-hand side of FIG. 6;

FIG. 8 is a view similar to-FIG. 6, but with the handle of the circuitbreaker operating mechanism in an OFF position;

FIG. 9 is a side view of a locking plate of the circuit breakeroperating mechanism;

FIG. 10 is a side view of a right-hand handle plate member of thecircuit breaker operating mechanism;

FIG. 11 is a side view of an actuating member of the circuit breakeroperating mechanism;

FIG. 12 is an end view of the actuating member of FIG. 11;

FIG. 13 is a bottom view of the actuating member of FIG. 1 1;

FIG. 14 is a side view of a cover-handle interlock member of the circuitbreaker operating mechanism;

FIG. 15 is a top view of the cover-handle interlock member of FIG. 14;

FIG. 16 is an end view of the cover-handle interlock member ofFIG. l4;

FIG. 17 is a top view of an interlock bracket mounted on the front coverof the motor starter unit;

FIG. 18 is a side view of the interlock bracket of FIG. 17;

FIG. 19 is an end view of the interlock bracket of FIG. 17;

FIG. 20 is a front view of a bracket mounted inside the front cover ofthe motor starter unit;

FIG. 21 is a top view of the bracket of FIG. 20;

FIG. 22 is an end view of the bracket of FIG. 20;

FIG. 23 is an end view of the interlock bracket of FIGS.

' 17-19 showing its relation to a portion of the actuating member ofFIG. 11-13 as they appear in broken lines in FIG. 5 and with thecircuitbreaker operating mechanism mounted as in FIGS. 1- 3;

FIG. 24 is an end view similar to FIG. 23, but showing the relation ofthe interlock bracket to a different portion of the actuating member fora mounting position of the circuit breaker operating mechanism as shownin FIG. 4; and

FIG. 25 is a fragmentary sectional view taken substantially along theline 25-25 of FIG. 3 but including a portion of a circuit breaker havingan operating handle connected to the circuit breaker operatingmechanism.

A motor starter unit 20 constructed in accordance with the invention isshown in FIGS. 1,2, and 5. The unit 20 is designed for use on electricalpanelboards of the type disclosed in U.S. Pat. No. 3,354,357issued Nov.21, 1967, and is mountable selectively on opposite sides of a centralbus bar stack of the panelboard without change of angular orientationwith respect to the panelboard.

The unit 20 includes'an open-front box 21 inwardly flanged at the frontand normally closed by a flanged cover 22 pivotally mounted on a leftside 21a of the box. The sides of the box 21 are generally L-shaped, aright side 21b being fragmentarily shown in FIG. 5, and the rear of thebox is defined by a stepped rear wall including a relatively deep wallportion 210 and a relatively shallow wall portion 21d connected by anormally horizontal wall portion 2le. Thus, the box 21 includes arelatively deep lower compartment 21] for housing the motor controllerand accessories, (contactor, control transformer, overload switch,etc.), which form no part of the present invention and are not shown,and a relatively shallow upper compartment 21g for housing an externalcircuit breaker operating mechanism 24 to be described. A moldedcasecircuit breaker 23 (FIG. 25) is normally mounted on a panelboard behindthe shallow compartment 21g, and the sides 21a and 21b of the box areslotted, as at a slot 21h in FIG. 5, to provide clearance for a circuitbreaker operating handle 25 when it is desired to replace a circuitbreaker 23 without disturbing the mounting of the box 21 on thepanelboard. The shallow rear wall portion 21d is provided with a centralscalloped aperture 21j (FIG. 1, 3, and 4) permitting access to load lineconnectors (not shown) of a circuit breaker, and the aperture 21includes opposed end slots 21k and 21m respectively joining the slots,such as the slot 2111 (FIG. 5), in the sides 21a and 21b of the box 21to permit passage of a circuit breaker operating handle 25 duringreplacement of a circuit breaker 23.

Two mounting brackets 26 are secured to the deep rear wall portion 21cadjacent opposite sides of the box 21, preferably by spot welding. Eachbracket 26 includes a pair of spaced mounting feet 26a projectingoutwardly beyond the respective side 21a or 21b of the box, and eachmounting foot 26a' is notched to provide a notch 26b.

When the motor starter unit 20 is to be mounted on the right-hand sideof a bus bar stack of an electrical panelboard of the type disclosed inthe aforementioned U.S. Pat. No. 3,354,357, the mounting feet 260adjacent the left side 21a of the box 21 are inserted beneath therearmost insulator of the bus bar stack, and the mounting feet 26aadjacent the right side 21b are secured to the mounting pan of thepanelboard respectively by a pair of screws (not shown) having headportions larger that the notches 26b and threaded shank portions whichfit within the notches 26b. Conversely, when the motor starter unit 20is to be mounted on the left-hand side of the bus bar stack, and themounting feet 26a adjacent the right side 21b of the box 21 are insertedbeneath the rearmost insulator of the bus bar stack, and the mountingfeet 26a adjacent the left side 21a are secured to the mounting pan ofthe panelboard respectively by a similar pair of screws (not shown).

Insulation is provided around the rearmost portion of the sidewalls ofthe box 21. Thus, a relatively thin sheet 28 of phenolic insulatingmaterial is secured to the right side 21b by a pair of round-headeddouble-pronged fasteners 30 and a pair of bent-over tang portions 26c ofthe respective bracket 26. An identical sheet 28 of insulating materialis similarly secured to the left side 21a. A sheet 32 of insulatingmaterial is secured to the wall portion 21e by four of the fasteners 30,and a similar sheet 33 of insulating material is secured to a bottomwall 21 of the box by four of the fasteners 30.

A latch member 34 is pivotally mounted on a pin 35 extending through theright side 21b of the box 21 and biased toward a cover latching positionby a compression spring 36. The latch member 34 extends through a slot22a in the cover 22 and has a latching surface 34a, which overlaps aportion of the front surface of the cover in the latching position. Thelatch member 34 also has a hole 34b for receiving a hasp of a padlock.

Mounted on the cover 22 are a START pushbutton 38, a green ON pilotlight 39, a STOP pushbutton 40, a red OFF pilot light 41, and'a RESETpushbutton 42, all associated with the motor controller in thecompartment21f, incidental with respect to the present invention, andnot herein further described. For a description of the start and stoppushbuttons, reference may be had to U.S. Pat. No. 3,370,481.

. The external circuit breaker operating mechanism 24 is external of themolded case circuit breaker 23 and is mountable in two differentpositions in the compartment 21g as shown in FIGS. 3 and 4, and when itis changed from one of the positions to the other, it is rotated through180 to reverse it endfor-end, and also shifted laterally of the box 21.The cover 22 is provided with an elongated slot 22b (FIG. 1) whichextends nearly the full width of the box 21 to accommodate an externalhandle 44 of the mechanism 24 in the two different mounting positions ofthe mechanism.

The mechanism 24 is shown separately in FIGS. 6 and 7 and includes agenerally U-shaped housing 46 having a pair of spaced outwardly bentmounting feet 46a and 46b extending from one side and a similar pair ofmounting feet 460 and 46d (FIGS. 3 and 4) extending from the other side.Each mounting foot of the housing 46 has a keyhole-shaped aperture 46e(FIGS. 3 and 4) for receiving a mounting screw.

A mounting pin 48 (FIGS. 6 and 7) extends through both sides of thehousing 46 and is retained therein by an enlarged head portion at oneend and a pushnut 49 at the other end. A flat, generally triangularlocking plate 50 best shown in FIG. 9 is mounted on the pin 48, whichextends through a suitable hole 50a in the plate 50. The locking plate50 is held against movement axially of the pin 48 by a pair of tubularspacers 52 (FIG. 7) mounted on the pin 48 within the housing 46 anddisposed respectively on opposite sides of the locking plate 50. Aportion 50b of the locking plate extends outwardly of the housing 46through a suitable slot in a raised boss portion 46f (FIG. 6) of a bightportion 46g (FIG. 7) of the housing and is provided with a slot 500suitable for receiving a hasp of a padlock to lock the handle 44 in anOFF position. A guide slot 50d (FIG. 9) is provided in the locking platewithin the housing 46 for a purpose explained hereinafter.

The handle 44 includes a pair of generally triangular righthand andleft-hand handle plate members 54 and 55 (FIGS. 6 and 7) pivotallymounted on the pin 48 and disposed respectively on opposite sides of thelocking plate 50 and between the tubular spacers 52. The right-handhandle plate member 54 is best shown in FIG. and is provided with a hole54a for receiving the pin 48, a hole 54b suitable for receiving a haspof a padlock to lock the handle 44 in an OFF position, and a slot 540for receiving a drive pin 64 for a purpose hereinafter explained. Anexternal handle portion 54d of the handle plate member 54 extendsoutwardly of the housing 46. The handle plate member 55 is identical tothe handle plate member 54 except that free end portions 54e and 55a ofthe external handle portions 54d and 55d are outwardly offset inopposite directions, as best shown in FIG. 7. A molded plastic hand gripmemberformed of two halves 56 and 57 (FIG. 6) is secured to the free endportions 54e and 55e by a rivet 58.

An actuating member 60 for operating a pivotable operating handle of anelectric circuit breaker, such as shown on the electrical panelboard ofthe aforementioned U.S. Pat. No. 3,354,357, is reciprocally mounted inthe housing 46 for movement by operation of the handle 44. The actuatingmember 60 also forms part of an interlock for the cover 22, ashereinafter explained.

The actuating member 60 is best shown in FIGS. ll, 12, and 13. Withreference to the end view of FIG. 12, the actuating member comprises agenerally U-shaped member including a bight portion 60a, a pair ofspaced parallel side portions 60b and 600, and a pair of inwardly offsetfree end portions 60d and 60e joined respectively to the side portions60b and 60c respectively by a pair of angularly extending offsettingportions 60f and 60g. An extended portion of the free end portion 60d isbent outwardly to form a tongue 60h cooperable with an interlock bracket62 (FIGS. 1, 5, 17, 18, and 19) on the cover 22 as hereinafterdescribed. Further, an extended portion of the free end portion 60c isbent outwardly to form a tongue 60j also cooperable with the interlockbracket 62 as hereinafter described. The tongue 60] is reversely curvedat an outer end portion 60k.

As can be seenin FIG. 11, the offsetting portion 60f and the free endportion 60d are longer than the side portion 60b in a direction parallelto the bight portion 60a, being partially defined by an inclined edgeportion 60m. The offsetting portion 60g and the free end portion 60c aresimilar respectively to the offsetting portion 60f and the free endportion 60d in this respect. The free end portions 60d and 602 areprovided respectively with a pair of aligned holes 60!: and 60p for thereception of the drive pin 64 (FIGS. 6 and 7) which also extends throughthe guide slot 50d (FIG. 9) in the locking plate 50, the slot 54c (FIG.10) in the handle plate member 54, and a slot (not shown) in the handleplate member. 55 similar to the slot 54c. The drive pin 64 is retainedin place by an enlarged head portion (not shown) at one end and apushnut 65 at the other end.

The side portions 60b and 600 are provided respectively with a pair ofaligned holes 60q and 60r for the reception of a guide pin 66 which alsoextends through both sides of the housing 46 and is retained therein byan enlarged head portion at one end and a pushnut 67 at the other end.Each side of the housing 46 is provided with a guide slot, such as theslot indicated by numeral 68 (FIG. 6), in which the pin 66 is received.I

As the hand grip member 56-57 is moved back and forth between ON and OFFpositions, the handle plate members 54 and 55 pivot on the mounting pin48 and move the drive pin 64 along the guide slot 50d in the lockingplate 50, and the drive pin 64 moves the actuating member 60 back andforth within the housing 46 as the actuating member is guided bymovement of the guide pin 66 in the guide slot 68 and the correspondingguide slot (not shown) in the opposite side of the housing 46. Anopenend slot 69 (FIG. 6) is provided in one side of the housing 46 toaccommodate the tongue 60h, and a similar open-end slot 70 (FIG. 7) isprovided in the other side of the housing to accommodate the tongue 60j.A tension spring 72 (FIGS. 1, 2, 6, and 7) is anchored at one end on thedrive pin 64 and at the other end on the housing 46 adjacent the openend of the slot 70 to bias the actuating member 60 and the handle 44toward OFF position.

The actuating member 60 is provided with a pair of tongues 60s and 60!(FIG. 13) extending outwardly from the bight portion 60a for a purposeexplained hereinafter. A spacer plate 74 for a pair of resilientgripping members 75 is welded to the inside of the bight portion 60a. Agenerally rectangular aperture 60u is provided in the bight portion 60aand a similar aperture 700 is provided in the spacer plate 74 for thereception of an operating handle of a molded case circuit breaker, suchas the operating handle 25 of the circuit breaker 23, and resilientgripping thereof by the gripping members 75. The spacer plate 74 addssufficient thickness to the bight portion 60a to enable the resilientgripping members 75, made of spring wire, to be retained in place byfriction. Further, the spacer plate 74 may be made of hardened steel toprevent undue wear on the bight portion 60a.

A hood 76 is pivotally mounted on the housing 46 adjacent one endthereof by a pair of rivets 77 and 78. The hood 76 extends to the right,as viewed in FIG. 6, beyond the housing 46 to act as a filler plate inthe portion of the slot 22b of the cover 22 not filled by the housing 46in a particular mounting position of the circuit breaker operatingmechanism 24. The hood 76 is slotted to receive the boss portion 46f ofthe housing 46, and the projecting end portion is provided with acorresponding boss portion 76a. The pivotal mounting of the hood 76enables pivoting thereof to provide access to a load line connector (notshown) for the center pole of a three-pole circuit breaker, such as thecircuit breaker 23, mounted behind the compartment 21g when the circuitbreaker and the motor starter unit 20 are mounted on a panelboard.

Inside the housing 46, an interlock member 80 best shown in FIGS. 14,and 16 is pivotally mounted on the rivet 77. The member 80 includes aflat elongated body portion 80a, an inwardly offset mounting ear portion80b, and an outwardly offset cover-actuated driving arm portion 80c. Themounting ear portion 80b is provided with a hole 80d for reception ofthe rivet 77 and a hole 80e for reception of one end portion of atorsion spring 81 also mounted on the rivet 77 and having its other endportion held by a tang 46h bent inwardly from a side of the housing 46.The spring 81 biases the member 80 counterclockwise as viewed in FIG. 6.The left side of the housing 46 as viewed in FIG. 7 is provided with agenerally rectangular aperture 46j (FIG. 6) through which the drivingarm portion 80c extends, the aperture 46j being sufficiently large topermit a limited amount of pivotal movement of the member 80.

The member 80 is shown in FIG. 6 in the same position as that in whichit appears in FIG. 2, with the handle 44 in an ON position. When thecircuit breaker operating mechanism 24 is removed from the box 21, itnormally appears as shown in FIG. 8, with the handle 44 in an OFFposition and the member 80 pivoted counterclockwise from the position inwhich it appears in FIG. 6 to a position in which a surface 80f(FIGS. l4and 15) of the body portion 80a engages the tongue 60h of the actuatingmember 60. The member 80 is designed to prevent movement of the handle44 from the OFF to the ON position when the cover 22 is open. Withreference to FIGS. 8, l4, l5, and 16, upon attempted movement of thehandle 44 to ON position, the actuating member 60 moves to the left, andthe tongue 60h moves along the surface 80f until it engages a stopshoulder portion 80g, after which no further movement takes place. Whenthe cover 22 is closed, as shown in FIG. 2, it depresses the driving armportion 80c to move the stop shoulder portion 80g out of blockingrelationship with the tongue 60h and permits movement of the handle 44to ON position in which the tongue 60h engages a surface 80h (FIGS. 14,15, and 16) of the body portion 80a.

The interlock bracket 62 is best shown in FIGS. l7, l8 and 19 andincludes a generally flat, elongated rectangular mounting portion 62ahaving a generally square aperture 62b therein for reception of aslotted-head mounting and driving rivet 82 (FIG. 1). The cover 22 isdished inwardly around the head of the rivet 82 to provide a recesstherefor, the outer surface thereof being substantially flush with theremainder of the cover. The mounting portion 62a is provided with a slot620 adjacent the left end thereof as viewed in FIG. 17, forming a tabportion 62d which is offset outwardly from the major portion of themounting portion 620, as best shown in FIG. 18. Adjacent the other end,the mounting portion 62a is provided with a pair of spaced slots similarto the slot 62c, and the portion between the slots is bent inwardly toform a spring anchoring tongue portion 62e having an aperture 62f (FIG.19) therein in which one end portion of a tension spring 83 (FIGS. 1 and5) is anchored. An outwardly offset tab portion 62g is provided adjacentthe tongue portion 62e. The amount that the tab portions 62d and 62g areoffset is sufficient to enable them to bear against the inner surface ofthe cover 22 while the mounting'portion 62a bears against the inwardlydished portion (not shown in detail) of the cover 22 around the head ofthe rivet 82.

Extending inwardly from an upper edge portion of the mounting portion62a is an interlock portion 62h provided adjacent opposite endsrespectively with a pair of reversely curved tongues 62] and 62k, thetongue 62] being curved upwardly and the tongue 62k being curveddownwardly.

The shallow rear wall portion 21d of the box 21 is provided with twospaced parallel rows of four tapped holes in which a plurality of screws84 may be captively mounted. The mounting feet 46a, 46b, 46c and 46d ofthe housing 46 are respectively slipped over the heads of four of thescrews 84 and the screws tightened over the small portions of thekeyhole slots to secure the circuit breaker operating mechanism 24 inplace. When the motor starter unit 20 is to be mounted to the right of abus bar stack as shown in the aforementioned U.S. Pat. No. 3,354,357,the operating mechanism 24 is mounted as shown in FIGS. 1-3 using thefour screws 84 closer to the left side 21a of the box 21. When the motorstarter unit 20 is to be mounted to the left of a bus bar stack, theoperating mechanism 24 is mounted as shown in FIG. 4 using the fourscrews 84 closer to the right side 21b of the box 21.

The tongues 60.: and 60t on the actuating member 60 are provided tointerfere with a circuit breaker handle if an attempt is made to mountthe operating mechanism 24 incorrectly in a central position using thecentral four screws 84. If the tongues. 60.: and 60t were not provided,the actuating member 60 could be placed next to a circuit breakerhandle, such as the handle 25, in an incorrect central mounting of theoperating mechanism 24, rather than over the handle 25 using theaperture 60u, and the actuating member 60 could then push the circuitbreaker handle 25 to an ON position, but would not be able to pull itback to an OFF position, and an OFF position of the handle 44 would thengive a false indication of the position of the circuit breaker handle25.

A bracket 85 best shown in FIGS. 20, 21, and 22 is rigidly secured tothe inside of the cover 22 and includes a generally flat rectangularplate 85a slotted at opposite ends to provide tab portions of which atab portion 85b is bent inwardly substantially ninety degrees andprovided with a hole 85c through which the other end of the tensionspring 83 is anchored, and a second tab portion 85d generally diagonallyopposite the tab portion 85b is bent inwardly through a lesser angle.The spring 83 tends to rotate the interlock bracket 62 and rivet 82clockwise as viewed in FIG. 1, the tab 85d serving as a stop againstwhich the tab portion 62g abuts.

When the operating mechanism 24 is mounted as shown in FIGS. 1-3 and thecover 22 is closed and the handle 44 in in ON position, the tongue 60hof the actuating member 60 is in alignment with the curved tongue 62j asit appears in FIG. 1 and the curved tongue 62j is hooked in back of thetongue 60h as shown in FIG. 23 to prevent opening of the cover 22.However, a knowledgeable person may defeat the interlock so as to beable to open the cover 22 with the handle 44 in ON position by turningthe rivet 82 with a tool such as a screwdriver counterclockwise asviewed in FIG. 1 to rotate the curved tongue 62] downwardly (to the leftin FIG. 23) and out from in back of the tongue 60h.

When the operating mechanism is mountedas shown in FIG. 4 and the cover22 is closed and the handle 44 is in ON position, the tongue 60j of theactuating member 60 is in alignment with the curved tongue 62k as itappears in FIG. 1 and the curved tongue 62k is hooked in back of thecurved outer end portion 60k of the tongue 60 as shown in FIG. 24 toprevent opening of the cover 22. However, a knowledgeable person maydefeat the interlock so as to be able to open the cover 22 with thehandle 44 in ON position by turning the rivet 82 with a tool such as ascrewdriver counterclockwise as viewed in FIG. 1 to rotate the curvedtongue 62k upwardly (to the right in FIG. 24) and out from in back ofthe curved outer end portion 60k of the tongue 60].

Thus, regardless of the position in which the operating mechanism 24 ismounted, the cooperation between the interlock bracket 62 and theactuating member 60 prevents opening of the cover 22 when the handle 44is in ON position, except by defeat of the interlock. Further,regardless of the position in which the operating mechanism 24 ismounted, the cooperation between the actuating member 60 and theinterlock member prevents movement of the handle 44 to ON position whenthe cover 22 is open.

Iclaim:

A motor starter unit comprising an open-frontbox mountable selectivelyon opposite sides of but in the same relative angular relationship witha stack of bus bars of an electric circuit breaker panelboard, a frontcover pivotally mounted on the box, an interlock bracket mounted on theinside of the cover, and an external circuit breaker operating mechanismmountable in the box selectively in two linearly and angularly displacedmounting positions in accordance with a selected mounting position ofthe box, the operating mechanism including a housing, an external handlepivotally mounted on the housing and movable selectively to ON and OFFpositions, and an actuating member reciprocally mounted in the housing,connectible to an operating handle of a molded-case circuit breaker, andreciprocable by movement of the external handle, the actuating memberhaving a first portion cooperable with a first portion of the interlockbracket when the operating mechanism is in one of its mounting positionsin the box to prevent opening of the cover when the external handle isin ON position, and the actuating member having a second portioncooperable with a second portion of the interlock bracket when theoperating mechanism is in the other of its mounting positions in the boxto prevent opening of the cover when the external handle is in ONposition.

2. A motor starter unit as claimed in claim 1 wherein the interlockbracket is keyed to a driving rivet pivotally mounted on the cover andturning of the driving rivet in one direction when the operatingmechanism is in either of its mounting positions in the box moves theinterlock bracket out of cooperable relationship with the actuatingmember to enable the cover to be opened with the external handle in ONposition.

3. A motor starter unit as claimed in claim 2 including a positioningbracket rigidly secured to the inside of the cover and a tension springconnected at opposite ends respectively to the interlock bracket and thepositioning bracket and rotatively biasing the interlock bracket againstthe positioning bracket.

4. A motor starter unit as claimed in claim 1 including an interlockmember pivotally mounted on the housing of the operating mechanism andbiased toward an operative position wherein it interferes with theactuating member and prevents movement of the external handle to ONposition when the cover is open, the interlock member being pivoted toan inoperative position by the cover upon closing of the cover.

5. A motor starter unit as claimed in claim 1 wherein the cover isprovided with an elongated slot to accommodate the external handle inthe two mounting positions of the operating mechanism.

6. A motor starter unit as claimed in claim 5 including a hood pivotallymounted on the housing of the operating mechanism and extending beyondthe housing to form a filler plate for the portion of the slot not takenup by the housing in the particular mounting position of the operatingmechanism.

7. A motor starter unit as claimed in claim 1 wherein the box has arelatively deep compartment for housing a motor controller and arelatively shallow compartment for housing the operating mechanism.

8. A motor starter unit as claimed in claim 7 wherein each of oppositeside portions of the box partially defining the shallow compartment isprovided with a slot providing clearance for an operating handle of acircuit breaker.

9. A motor starter unit as claimed in claim 8 wherein a relativelyshallow rear wall portion of the box partially defining the shallowcompartment is provided with a central aperture and opposite end slotsrespectively joining the aperture to the slots in the side portions.

10. A motor starter unit as claimed in claim 1 including a pair ofresilient gripping members on the actuator for resiliently gripping anoperating handle of a circuit breaker.

2. A motor starter unit as claimed in claim 1 wherein the interlockbracket is keyed to a driving rivet pivotally mounted on the cover andturning of the driving rivet in one direction when the operatingmechanism is in either of its mounting positions in the box moves theinterlock bracket out of cooperable relationship with the actuatingmember to enable the cover to be opened with the external handle in ONposition.
 3. A motor starter unit as claimed in claim 2 including apositioning bracket rigidly secured to the inside of the cover and atension spring connected at opposite ends respectively to the interlockbracket and the positioning bracket and rotatively biasing the interlockbracket against the positioning bracket.
 4. A motor starter unit asclaimed in claim 1 including an interlock member pivotally mounted onthe housing of the operating mechanism and biased toward an operativeposition wherein it interferes with the actuating member and preventsmovement of the external handle to ON position when the cover is open,the interlock member being pivoted to an inoperative position by thecover upon closing of the cover.
 5. A motor starter unit as claimed inclaim 1 wherein the cover is provided with an elongated slot toaccommodate the external handle in the two mounting positions of theoperating mechanism.
 6. A motor starter unit as claimed in claim 5including a hood pivotally mounted on the housing of the operatingmechanism and extending beyond the housing to form a filler plate forthe portion of the slot not taken up by the housing in the particularmounting position of the operating mechanism.
 7. A motor starter unit asclaimed in claim 1 wherein the box has a relatively deep compartment forhousing a motor controller and a relatively shallow compartment forhousing the operating mechanism.
 8. A motor starter unit as claimed inclaim 7 wherein each of opposite side portions of the box partiallydefining the shallow compartment is provided with a slot providingclearance for an operating handle of a circuit breaker.
 9. A motorstarter unit as claimed in claim 8 wherein a relatively shallow rearwall portion of the box partially defining the shallow compartment isprovided with a central aperture and opposite end slots respectivelyjoining the aperture to the slots in the side portions.
 10. A motorstarter unit as claimed in claim 1 including a pair of resilientgripping members on the actuator for resiliently gripping an operatinghandle of a circuit breaker.